Need some help!

Why am I getting this error:

ERROR:Xst:528 - Multi-source in Unit <waittime> on signal <z>
Sources are:
Signal <z> in Unit <waittime> is assigned to GND
ERROR:Xst:415 - Synthesis failed
CPU : 1.72 / 2.52 s | Elapsed : 2.00 / 3.00 s

I have a very simple schematic with waittime going out to an output
marker.

waittime:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

-- Uncomment the following lines to use the declarations that are
-- provided for instantiating Xilinx primitive components.
--library UNISIM;
--use UNISIM.VComponents.all;

entity waittime is
Port ( z : out std_logic);
end waittime;

architecture Behavioral of waittime is

begin
z <= '1' after 500000000 ns;

z <= '0' after 500000000 ns;

end Behavioral;


I am using a CR-II c256 and ISE 6.3.03i.

Any help would be appreciated!

Thanks,
Brian

bhiggins@umr.edu

Brian
Looks like your code is meant for simulation purposes. And you have 2
concurrent signal assignment statements on "z" which is z <= '1' follwed
by z <= '0'. thats why you are getting the multisource error.
Doing something like z <= not z after 50 ns woulg give you a toggling
signal "z". Make sure you initialize "z" to '0'. After clauses are for sim
purposes only. I am assuming you are just doing a simulation here.

fpgawizz

I am actually wanting the cpld to toggle the signal for real not for
just simulation. What should I use instead of "after"? How should I
toggle it so I do not get the multisource error?

Thanks in advance,
Brian

bhiggins@umr.edu

You have to use a clock to do your toggling. You can have two states in a
state machine where in state 1, you set z to 0, and in state 2 z is set
to 1 and this state machine is clocked by your 50 ns clock. z would then
be a toggling signal.

fpgawizz

wrote:

> ERROR:Xst:528 - Multi-source in Unit <waittime> on signal <z>

You are driving a value to one signal from more than one process. (Note
that every concurrent statement ist also considered as a process.)


> use IEEE.STD_LOGIC_ARITH.ALL;
> use IEEE.STD_LOGIC_UNSIGNED.ALL;

Just a note: It is not recommended to used these libraries, as their
implementation dependts on the simulator / synthesizer. Use
IEEE.Numeric_std.ALL instead.



>
> begin
> z <= '1' after 500000000 ns;
>
> z <= '0' after 500000000 ns;
>
> end Behavioral;

Two concurrent statements driving z.

process -- no sensitivity list - triggered at simulation start
begin
z <= '1' after 500000000 ns;
z <= '0' after 500000000 ns;
wait; -- uncomment to execute the process again after end
end process;


Note: This is only for simulation. the after-clause is NOT synthesizable.

Whats your intention for this piece of code? Is it a clock or just a
signal, that should be high and go to low later.
If it is a clock - take an internal clock generator from you FPGA or use
the clock via a FPGA input pin.
I it is a signal - you need a clock with a period suitable for you
desired "delays". Test e.g. for the rising_edge(clock).

Ralf

Ralf Hildebrandt